Boaz is a great warrior not because he actually participates in any wars but because he is a warrior for God.
He first meets Ruth when she is gathering grain behind the harvesters and in a compassionate way asks her to stay, eat, drink and continue gathering grain. I’m sure at that time, it took the full power of the Lord compelling him to help a more or less beggar. Ruth then asks Boaz why he was compelled to help her since she is a foreigner. He explains that he has learned of Ruth’s faithfulness and that he prays the God of Israel will bless Ruth for her loyalty. This example show that Boaz is living the life of a Godly man by helping someone that wouldn’t traditionally be helped. Ruth then attempts to lay with Boaz in the threshing room but he shows his true character by not attempting to take advantage of Ruth. This is portion truly shows that Boaz was a man following God and not his own will.